Recently, amorphous semiconductor photosensors prepared by a radio-frequency glow discharge method have been developed for large-area low-cost thin-film image sensors, for example, for the contact-type linear sensor of a compact facsimile machine, or for the photoreceptor of a laser beam printer.
Basically, there are two kinds of a-Si:H photosensors, namely, Schottky or the p-i-n photodiode and the photoconductor type. However, both of these kinds of photosensors suffer from low photocurrent output and low S/N ratio, due to a lack of amplification. Recently, we have demonstrated that the amorphous silicon n.sup.+ -i- (p.sup.+)-i-n.sup.+ thin-film bulk barrier phototransistor exhibits high gain and high response speed. In this specification, the successful development of a new type of glass/ITO/a-Si(n.sup.+ -i-p.sup.+)/a-SiC(i-n.sup.+)/Al heterojunction bulk barrier phototransistor with wide-bandgap a-SiC emitter is described. This is an alternative type of the recently reported glass/ITO/a-SiC(n.sup.+ -i-p.sup.+)/a-/Si(i-n.sup.+)/Al device.